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Abstract

Microstructure fibers with multiple submicron cores are used to frequency-convert unamplified 0.3-nJ, 80-fs pulses of 800-nm Ti: sapphire laser radiation to the spectral range of 400–500 nm. This frequency-upconverted radiation is then employed to induce reversible changes in the absorption spectrum of spiropyran molecules through photochromic transformations in a solid-phase spiropyran/PMMA sample. Microstructure fibers are thus shown to enhance the capabilities of low-power femtosecond lasers, making unamplified ultrashort pulses suitable for photochemical and micromachining applications.

Generation of the blue (a) and green (b) anti-Stokes lines in submicron channels of a 5-cm-long MS fiber (shown in inset 1 to Fig. 3(a)) by 0.3-nJ, 80-fs pulses of 800-nm radiation. The insets show (inset 2 in Fig. 3(a)) the spectra of the blue anti-Stokes line at the input (line 1) and at the output (line 2) of the SP/PMMA sample; (inset 1 in Fig. 3(b)) decay of the PL signal, indicating the recovery of form-A spiropyran under the action of the green anti-Stokes line in the area pre-irradiated with the blue anti-Stokes line, switched off at t=0; (inset 2 in Fig. 3(b)) PL excited by the green anti-Stokes line, visualizing micromachining of a photochromic material by femtosecond Ti: sapphire laser pulses through two-photon photochromism.

Kinetics of the PL signal, visualizing the generation of form-B spiropyran in the SP/PMMA sample by the blue anti-Stokes line produced in the MS fiber. The inset shows the spectrum of PL from the blue-line-irradiated area of the SP/PMMA sample excited with 532-nm, 10-mW second-harmonic radiation of the cw Nd: YAG laser.